Various forms of semi-trailers presently being manufactured are referred to as "flats" in that they define a raised upper flat loading surface while other semi-trailers are termed "drop center trailers" inasmuch as the center load receiving portions thereof between the front and rear ends of the trailer are appreciably lowered relatively to the front and rear trailer ends.
"Flats" are conventionally utilized for carrying various forms of bulk equipment and supplies, whereas the "drop center trailers" are utilized primarily to carry heavy loads which may not be readily lifted to the high level of the load carrying surface of "flats". However, semi-trailers in many instances carry loads thereon in only one direction due to the unavailability of a return load on the same type being available. Furthermore, in many instances when a "drop center trailer" is utilized to carry a load in one direction, the only load which may be available therefor in the return direction comprises a load that may best be carried by a "flat". Accordingly, a need exists for an improved form of trailer which may be readily converted from a "flat" to a "drop center trailer".
Convertible trailers heretofore have been designed such as those disclosed in U.S. Pat. Nos. 1,719,587, 2,776,146, 2,970,861, 3,103,397, 3,319,393 and 4,092,039. However, these various forms of convertible and adjustable trailers are not capable of being readily completely transformed between "flat" and "drop center" trailer configurations.